[ Alan Griffiths ]
* ipc: add a protocol version to the wire protocol so that we can bump
it in future.
* graphics::nested: Handling of output configuration changes.
* graphics.nested: Hookup NestedDisplay to display change
notifications.

[ Eleni Maria Stea ]
* changed the GBMBufferAllocator constructor and class to use the
gbm_device instead of the GBMPlatform to remove the dependency from
the mg::Platform interface - this way we can use the
GBMBufferAllocator with the NativeGBMPlatform (nested mir).